1. Field of the Invention
The present invention relates to the field of microcomputer systems, in particular, this invention relates to the replacement of a microprocessor in a microcomputer system having a processor extension.
2. Description of the Related Art
In microcomputer systems, it is often desirable to increase system performance in order to increase the speed in which tasks are completed. A first known technique for increasing the performance of a microcomputer system is by replacing a microprocessor contained in the microcomputer system with a different microprocessor that provides such increased performance. Replacement of microprocessors is desirable because it is a cost effective in that other components in the microcomputer system are typically retained (e.g. the RAM memory, external disks, etc.). A second known technique for increasing the performance of a microcomputer system is through the use of processor extensions. Processor extensions are special purpose processing components, e.g. a math co-processor, that perform a predefined set of operations at processing speeds significantly greater than that of general purpose microprocessors. Processor extensions receive operation codes and operands from a general purpose microprocessor, perform the desired operation and return the results to the general purpose microprocessor. All of this may occur while the general purpose microprocessor is performing some other task.
Mathematical operations are a common predefined set of operations implemented on a processor extension, and are referred to as a Numeric Processor Extension (NPX). Such NPX devices include the Intel.RTM. 80287 and 80287XL Numeric co-processors available from the Intel Corporation of Santa Clara, Calif. The 80287 and 80287XL are designed for use with the Intel 80286 line of general purpose microprocessors. The 80287 and 80287XL differ in that the 80287XL has a greater number of numeric operations it may perform. Otherwise, a computer system design utilizing either device would be identical.
Typically, an NPX is designed to operate closely with a particular microprocessor. Operate closely refers to design aspects of both the microprocessor and the NPX which would facilitate fast communication and coordination between the two components. This would include dedicated I/O ports as well as dedicated handshaking lines on the respective components. In the case of the aforementioned 80287 and 80287XL, the microprocessor that they operate closely with is the Intel 80286.
It is common for different microprocessors to have different methods and techniques for coordinating operations and communicating with an NPX. This occurs because a standard interface does not exist between a microprocessor and NPX. This creates additional requirements for replacing a first microprocessor with a second microprocessor. Typically, in such a replacement, the NPX would also have to be replaced.
Known microprocessor devices are members of "families" of such devices. A microprocessor family, for example the 80286 "family" of microprocessors, contains function and performance characteristics that are substantially similar. Differences lie in chip packaging and/or operational specifications. Other differences include CPU clock rates or the size of the address path. The 80286 family of microprocessors are described as 16-bit microprocessors because they have 16-bit internal architectures and are designed for microcomputer systems with 16-bit wide data paths.
The Intel.RTM. 80386 family of microprocessors have 32- bit internal architectures, but individual members may be used with microcomputer systems that have varying sized data paths. A member of the 80386 family that is designed for use in microcomputer systems with 32-bit wide data paths is the 80386DX.TM.. Alternatively, the 80386SX.TM. has a 32-bit internal architecture but is designed to be used with microcomputer systems that have a 16-bit data path. The 80386 family of microprocessors is distinguishable from the 80286 in that the 80386 family has: a greatly increased addressing range; the ability to accommodate operands with a greater number of bits and may perform operations at a greater speed. The Intel 80286 and 80386 family of microprocessors are described in detail in the publication Microprocessors, order No. 230843-007 available from the Intel Corporation of Santa Clara, Calif.
Known microcomputer systems that utilize an 80286 or compatible microprocessor and have 16-bit data paths are the IBM PC/AT and PS/2.RTM.; models 25-286, 50, 50-Z, 60, and 30-286 (hereinafter qualifying PS/2 systems); all available from the IBM Corporation of Armonk, N.Y., or PC/AT or PS/2 compatible systems. Technical specifications concerning the PC/AT and PS/2 system design are available from the IBM Corporation. In the aforementioned microcomputer systems, the use of the 80287 or 80287XL as a numerics processor extension is optional. The user of the microcomputer system would optionally install the 80287 or 80287XL if the application software that they used required or would benefit from it. In such systems, a chip socket is provided for electrical coupling of the processor extension.
Coupling an 80386DXTM.TM. a PC/AT or compatible microcomputer system is known in the art. The Intel Corporation offers a product under the name InBoard.TM., which provides for the replacement of the 80286 with 80386DX. With the InBoard, an 80386DX is coupled to a Printed Circuit Board (PCB). The PCB contains it's own RAM memory, processor extension socket for an 80387 Numeric Co-processor, and other support circuitry. The InBoard is coupled to the PC/AT microcomputer system through one of a plurality of I/O slots on the PC/AT microcomputer system motherboard. A ribbon cable with an 80286 socket compatible plug, is used to electrically couple the PCB with the 80286 socket. Detailed technical information about the InBoard product is available from the Intel Corporation.
The InBoard design does not make use of processor extensions or all of the RAM memory that currently exist on the PC/AT motherboard. As a result, these components are unneeded. This results in increased costs and wasted assets. The increased costs are in requiring the purchase of new RAM memory and an 80387 NPX. The wasted assets are the unneeded RAM memory and processor extension (i.e. on 80287 or 80287XL).
Coupling an 80386DX to a PC/AT or compatible microcomputer system using the InBoard design requires much support circuitry because of the inherent architectural differences between the 80386DX and the 80286 families. Such difference include the additional addressing and data lines in the 80386DX. Additionally, since the InBoard design requires an I/O slot on the PC/AT system, it's use is limited to systems with an available I/O slot. The InBoard design is further limited in that it cannot be used-in non-PC/AT compatible systems.
Utilizing an 80386DX Microprocessor with an 80287 Numeric co-processor is described in general in the above referenced publication Microprocessors. However, it is important to note that the description in the reference is directed to the 80386DX microprocessor and not the 80386SX microprocessor. An important distinction between an 80386DX and and 80386SX is that the 80386DX microprocessor has the ability to recognize the 80287 as an NPX and thus communicate with 80287 in a compatible manner. Further, the interface described in the publication assumes that the microcomputer system is being designed specifically for the 80386DX, i.e. it is not intended to be a design for an interface module to an existing microcomputer system. The reference fails to contemplate utilizing a 80386SX replacing a 80286 in a Microcomputer system with an 80287 installed.
As described above, the 80386SX is designed to operate in microcomputer systems with 16-bit data paths. Thus, in order to gain the benefits of the 80386 family of microprocessors in a currently existing microcomputer system, it would be desirable to replace the 80286 microprocessor in an IBM PC/AT, PS/2 qualifying or compatible microcomputer systems, with an 80386SX. Although the 80286 and the 80386SX can both be utilized on a microcomputer system with 16-bit wide data paths, the two differ in many other respects. These differences include pin configurations, internal cycle times, exception handing, and operation with NPX devices.
It is an object of the present invention to provide for replacement of an 80286 with an 80386SX in a PC/AT, PS/2 qualifying or compatible system when an 80287 or 80287XL has been optionally installed. Further, it is an object of this invention to provide such a method that does not require an I/O slot on the PC/AT or compatible system. The objects of the invention are desirable because it would reduce the consumer cost of obtaining functionality and performance increases of the 80386 line of microprocessors as well as extend the useful life of PC/AT or PS/2 and compatible microcomputer systems.